EVOLUTIONARY RELATIONSHIPS, HOST-RANGE AND GEOGRAPHICAL-DISTRIBUTION OF CAMALLANUS RAILLIET AND HENRY, 1915 SPECIES (NEMATODA, CAMALLANINAE) FROM CLAWED TOADS OF THE GENUS XENOPUS (ANURA, PIPIDAE)

Representatives of the genus Camallanus Railliet & Henry, 1915 occur m ainly in teleost fishes, although a significant number of species have also been recorded from anuran amphibians. The taxonomy, host range, geographical distribution and phylogenetic relationships of Camallanus spp. from African clawed toads (Xenopus spp.) are reviewed. Besides C . kaapstaadi Southwell & Kirshner, 1937, which shows a widespread dist ribution in sub-Saharan Africa and occurs in X. laevis subspecies, X. wittei, X. fraseri-like toads, X. borealis and X. muelleri, three new species were found: C. siluranae n. sp. from X. tropicalis in west Afr ica, C. macrocephalus n. sp, from X. borealis in Kenya, and C. xenopod is n. sp. from X. laevis laevis in South Africa and X. borealis in Ken ya. C. johni Yeh, 1960 described from Xenopus sp. in Tanzania is consi dered a species inquirenda. C. kaapstaadi and C. macrocephalus are ver y closely related and both occur in the oesophagus of their hosts, unl ike other Camallanus spp. which are found in the intestine or more rar ely the stomach. Some of the unusual morphological features of these s pecies may be an adaptation to attachment in the oesophagus. The host of C. siluranae, X. tropicalis, belongs to a separate species group (a s has been established by recent molecular and cytological studies) to those of C. kaapstaadi, C. macrocephalus and C. xenopodis. Morphologi cal affinities suggest that Camallanus spp. from clawed toads are not monophyletic with those from other amphibians and that C. siluranae is distantly related to, and probably not monophyletic with the remainin g species from clawed toads. The Camallanus fauna of Xenopus spp. may thus be derived from at least two independent colonisations, of differ ent host clades, by parasite lineages occurring in teleost fishes.